Coffee bean grinders typically include a hopper in which coffee beans are placed to be delivered to a grinding apparatus. The grinding apparatus grinds the coffee beans and delivers ground coffee beans to a receptacle. The receptacle can be part of a coffee brewing machine such that the receptacle is a brew basket or similar receptacle. Coffee bean grinders can also be made separately from the coffee brewing machine where the ground coffee is taken from the receptacle and poured into a brew basket.
The lack of coffee beans in the hopper of the coffee bean grinder should be detected as soon as possible. If the lack of coffee beans is not detected in time, a motor that is part of the grinding apparatus could overheat if it runs under no load conditions for an extended period of time. Some known coffee bean grinders stop running the motor either at the time that a desired amount (e.g., weight) of coffee has been ground or upon detecting that no coffee beans are in the hopper any longer.
Weight sensors have been used to determine that the desired amount of coffee beans has been ground. For example, one known coffee bean grinder includes a control circuit having a selector for selecting a desired weight of ground coffee to be produced. A weight sensor positioned beneath a receptacle repeatedly weighs the ground coffee accumulating in the receptacle and transmits the actual weight signal to the control circuit. The actual weight is then compared to the selected weight of ground coffee to be produced, and the control circuit stops the grinding mechanism when the measured weight equals the selected weight. There is no mention, however, of stopping the motor when there are no coffee beans in a hopper that feeds the grinding mechanism of the coffee bean grinder.
The detection of a lack of coffee beans in the hopper of a coffee bean grinder has been performed through using optical sensors positioned within the hopper. These optical sensors, however, can be covered with dust as the coffee bean grinder is used more and more often. Other known coffee bean grinders monitor the electrical current running through the motor and conclude from the magnitude of the current drawn by the motor the absence of coffee beans in the hopper. The problem with this method of detection is that if one of the gears in the grinding mechanism becomes stuck and an output shaft of the electrical motor no longer rotates, the magnitude of the current drawn by the motor could increase and lead to a conclusion that the hopper is empty when in fact it is the motor that is stalled.